1. Field of the Invention
The present invention relates to a power transmission apparatus adapted for an optical apparatus such as a camera or the like.
2. Description of Related Art
Some cameras are provided with power transmission apparatuses for transmitting a film transporting power to a lens barrel driving mechanism or a charging member of a shutter mechanism. FIG. 4 shows, by way of example, the arrangement of a charging mechanism which is one of such power transmission apparatuses.
Referring to FIG. 4, a sprocket 1 is arranged to engage perforations provided in a film 2 and to be caused to make one rotation clockwise when the film 2 is transported to the right as viewed in FIG. 4 to an extent corresponding to one frame thereof. A pulse base plate 3 is arranged to rotate integrally with the sprocket 1. Pulse contact pieces 4 and 5 are in sliding contact with the pulse base plate 3 and are arranged to output two ON and OFF pulses from them while the sprocket 1 and the pulse base plate 3 make one rotation. Pulse plate 3 and pulse contact pieces 4 and 5 thus comprise a determination device which determines a rotating position of a first toothed wheel (sprocket gear 6, discussed below). These ON and OFF pulses are sent to a control device (not shown). The control device causes a film transporting action to come to a stop upon receipt of the ON pulse for the second time after the commencement of the film transporting action, so that the film transporting action for one frame is completed.
A sprocket gear 6 is arranged to rotate integrally with the sprocket 1. The sprocket gear 6 is arranged to engage with an idle gear 7, which, in turn, is arranged to engage with a charge gear 8, which is a toothed wheel. A charge cam 9 is rotatably mounted coaxially with the charge gear 8. As shown in FIG. 5, the charge gear 8 is provided with one-way cams 8a and 8b, and the charge cam 9 is provided with cam projections 9a and 9b, which are arranged to engage with and disengage from the one-way cams 8a and 8b. The charge gear 8 is urged by a spring 10 to move toward the charge cam 9. When the charge gear 8 rotates clockwise as viewed in FIG. 5, the cam projections 9a and 9b mesh with the one-way cams 8a and 8b, so that the rotation of the charge gear 8 is transmitted to the charge cam 9, and both the charge gear 8 and the charge cam 9 rotate integrally. When the charge gear 8 rotates counterclockwise, on the other hand, the cam projections 9a and 9b slip on the tapered parts of the one-way cams 8a and 8b, so that the rotation of the charge gear 8 is not transmitted to the charge cam 9, and, therefore, the charge cam 9 does not rotate in that instance.
A charge lever 11 is rotatably mounted on a shaft 12. The charge lever 11 is urged by a spring 13 to swing counterclockwise as viewed FIG. 4 and is thus caused to abut on a stopper 14. In FIG. 4, reference numeral 15 denotes a charging member provided for a shutter or the like (not shown). Shutter charging member 15 is thus a component of optical apparatus, such as a camera.
In the power transmission apparatus configured as described in the foregoing, when the film 2 is transported to the right, as viewed in FIG. 4, to cause the sprocket 1 to rotate clockwise, the charge gear 8 is caused through the sprocket gear 6 and the idle gear 7 to rotate clockwise. The clockwise rotation of the charge gear 8 causes the charge cam 9 to rotate integrally with the charge gear 8, i.e., toothed wheel 8 is integrally provided with charge cam 9 which is a member for a charging operation. When the charge cam 9 has rotated 180 degree from the state shown in FIG. 4, a cam part 9c of the charge cam 9 comes to push a projection 11a of the charge lever 11, so that the charge lever 11 is caused to rotate in the clockwise direction.
When the charge lever 11 rotates in the clockwise direction, an end part 11b of the charge lever 11 causes the charging member 15 to move to the left, thereby performing a charging action. Charging member 15 accordingly is an operating device which performs a predetermined operation (charging) according to a rotating position of a second toothed wheel (gear 8). Charging member 15 is thus a device for a charging operation, particularly, a shutter charging operation. At a point of time at which the charging action is completed, the projection 11a of the charge lever 11 overrides the cam part 9c of the charge cam 9, and the charge lever 11 is brought back to the state shown in FIG. 4 by the urging force of the spring 13. After the return of the charge lever 11, the phase of the pulse base plate 3 takes a position where the ON pulse is outputted for the second time through the pulse contact pieces 4 and 5, and the film transporting action for one frame comes to an end.
In the power transmission apparatus described above, it would become impossible to operate the shutter or the like unless the charging action is adequately completed before the completion of the film transporting action. Therefore, the phase of the pulse base plate 3 which generates pulses for controlling the film transporting action and the phase of the charge cam 9 provided for the charging action must be matched with, or adjusted to, each other.
According to the conventional method for such phase matching or adjustment, marks 7a and 8c are provided respectively on the idle gear 7 and the charge gear 8. In assembling the camera, an end face 3a of a conductive pattern of the pulse base plate 3 is adjusted to one of the marks 7a of the idle gear 7. After that, the other mark 7a of the idle gear 7 is adjusted to one of the marks 8c of the charge gear 8.
However, since the phase matching work is performed simply through visual confirmation, these parts tend to be assembled in a state of having a phase deviation between them. Besides, in the event of such misassembly, the misassembly tends to be left undiscovered until the shutter or the like is actually operated. Upon discovery of such Disassembly, however, the camera must be disassembled for correction of the misassembly. This is a serious problem.
Further, in cases where these parts are assembled at such phases that cause the charging action to be finished earlier than a normal timing, the shutter or the like might begin to be operated at a point of time where the charging action at the next phase begins. Then, although the shutter can be operated, it is impossible to know whether the shutter operation is performed up to the end of a normal operating range. Despite such a state, the camera might be allowed to pass the process of assembly inspection without correcting the phase deviation of parts.